ABSTRACT. Carp were cultivated (from day 3 to 30 after hatching) in water with a nitrite concentration of 7 mg NO2-N dm-3. The results of histological studies confirmed pathological changes in the throat, gills, heart, blood, swim bladder, liver and kidneys. These changes mainly had an adverse impact on respiration and growth. The total length and weight of fish from water with nitrites was lower by 30 and 75%, respectively, and their survival rate was 62% (97% in the control group).